Silicon photonics is a baseline technology that may be applicable for addressing a bandwidth bottleneck occurring in relation to future electronic circuits and/or systems. Silicon photonic circuits are based on many different elementary devices that may be applied for manipulating light. In a usual scenario, many of these elementary devices operate based on a change in the refractive index of one of their constituent materials, by applying an electrical field or current thereto.
One of the main functions implemented in silicon photonic circuits is light modulation by converting an electrical signal into an optical signal. Additionally, it is anticipated that silicon photonic circuits will rely on resonant structures with defined critical dimensions. Deviation from such critical dimensions may occur due to variations in fabrication processing and/or due to variations in an operating temperature. It is, therefore, desirable to provide devices in silicon photonic circuits that offer compensation to variability at low speed, below kHz, and at low power, or that enable optical modulation with power consumption below 1 mW/Gbps. Ideally, such devices are fabricated with materials exhibiting a relatively large, linear electro-optic effect also known as Pockels effect.
It is known that functional oxides such as the perovskites, for example, barium titanate BaTiO3 and potassium niobate KNbO3, exhibit a variety of properties related to their crystal and electronic structures. Such properties include, for example, piezoelectricity, magnetoresistance, superconductivity and electro-optical activity. Whilst the use of such functional oxides in electro-optic modulators is known, integration within silicon photonic circuits has not yet been reported. By co-integrating active optical devices based on such functional oxides together with passive devices fabricated within silicon photonic circuits, particularly the unique electro-optical properties of such functional oxides could be exploited. In this regard, it is desirable that light coupling elements such as waveguides in the passive circuitry are in relatively close proximity to the active optical devices based on the functional oxides so that light coupling is enabled with increased efficiency and reduced loss. It is also desirable that active optical devices based on functional-oxide materials are placed in close proximity to electronic devices in the circuitry to enable higher speed operation.
In order to be used in respect of devices and/or applications exhibiting reduced power consumption and/or increased efficiency light modulation, or compensation devices, it is desirable that a given functional-oxide material exhibits a relatively high Pockels coefficient. In this regard, it should be taken into consideration that the Pockels effect strongly depends on the crystalline axis of a functional-oxide layer incorporating the functional-oxide material. The requirements to integrate such a functional-oxide layer include: an ordered, epitaxially crystalline structure; relatively good insulation properties, which include avoiding the passage of any electrical currents through the functional-oxide layer; a given orientation of its crystalline axis with respect to the position of the electrodes that are used to modify the refractive index thereof so as to obtain a desired electro-optic effect, and reduced optical loss.
It is envisioned that devices based on such functional-oxides will be part of the silicon photonics technology. Silicon photonics chips will most likely contain optically active and passive devices co-integrated with electronic devices fabricated using standard CMOS technology. The electronic and photonic parts of the chips share the same front-end-of-line (FEOL) and back-end-of-line (BEOL) processes. FEOL may be defined as the part of the process where isolated devices are fabricated and BEOL as the part of the process where isolated devices are electrically interconnected.
It may be envisioned to place the functional oxide, crystalline layer during the FEOL that is used for fabricating silicon photonic devices and electronic devices. However, it is likely that such a layer and its interfaces would degrade when exposed to the relatively high temperatures used for FEOL processing, for example, during the activation anneal of the implanted source/drain region. In this regard, and by way of example, the processing temperatures used in the FEOL are T>700-800° C.
Alternatively, the functional-oxide, crystalline layer may be integrated into the BEOL of the process. This approach may, however, suffer from severe limitations on the thermal budget allowed on the integration and/or the processing of devices based on functional oxides since BEOL processing temperatures are lower, for example, T<400° C., compared to the temperatures that may be used for obtaining functional oxides such as perovskites with desired electro-optical properties, typically 500° C. Also, the functional-oxide, crystalline layer would be spatially remote from the silicon photonic layer/circuitry fabricated during the FEOL, so that the optical coupling between the silicon photonics and the functional-oxide layer may be virtually impossible.
Reference is now made to U.S. Pat. No. 7,718,516 B2, which discloses a method for growing SrTiO3 films with single (110) out of plane orientation upon a silicon surface substrate, comprising: crystallising an Sr-silicate interfacial layer epitaxially onto the silicon substrate under low oxygen pressure for about 1 to 5 minutes at a temperature of about 760 degrees centigrade to avoid oxidation of the silicon substrate, and depositing the SrTiO3 film at low oxygen pressure at a temperature of about 760 degrees centigrade.
WO 2011047370 A1 discloses a nanostructure comprising: a layer of a functional oxide deposited on a semiconductor substrate and having a substantially annular configuration, the functional oxide having a metal-insulator transition property that causes a drop in resistance of about four or more orders of magnitude at a predetermined temperature; and a nano-ring covering the layer of the functional oxide, the nano-ring comprising a metallic material.
WO 2013086047 A1 discloses an integrated semiconductor device having integrated circuits respectively formed on different semiconductor integrated dies, comprising: a carrier substrate structured to form openings on a top side of the carrier substrate; semiconductor integrated circuit dies fixed to bottom surfaces of the openings of the carrier substrate, each semiconductor integrated circuit die including a semiconductor substrate and at least one integrated circuit formed on the semiconductor substrate to include one or more circuit components, and each semiconductor integrated circuit die being structured to have a top surface substantially coplanar with the top side of the carrier substrate; and planar layers formed on top of the top surfaces of the semiconductor integrated circuit dies and the top side of the carrier substrate to include optical waveguides and photonic devices to provide (1) intra-die optical connectivity for photonic devices associated with a semiconductor integrated circuit die, or (2) inter-die optical connectivity for photonic devices associated with different semiconductor integrated circuits dies.
The document titled, “Active silicon integrated nanophotonics: ferroelectric BaTiO3 devices”, by Xiong et al. published at URL: http://arxiv.org/ftp/arxiv/papers/1401/1401.4184.pdf, pages 1 to 20, 2014, discloses nanophotonics circuits incorporating ferroelectric BaTiO3 thin films on a ubiquitous silicon-on-insulator (SOI) platform. Epitaxial, single-crystalline BaTiO3 grown directly on SOI and engineer integrated waveguide structures are grown that simultaneously confine light and an RF electric field in the BaTiO3 layer. Using on-chip photonic interferometers, a large effective Pockels coefficient of 213±49 pm/V was extracted, a value more than six times larger than found in commercial optical modulators based on lithium niobate. The monolithically integrated BaTiO3 optical modulators showed modulation bandwidth in the gigahertz regime, which was considered to be promising for broadband applications.
Other previously-proposed devices and/or systems are disclosed in the documents: “Epitaxial integration of perovskite-based multifunctional oxides on silicon”, by Baek et al. published at Acta Mater (2012), URL: http://dx.doi.org/10.1016/j.actamat.2012.09.073, “Integration of functional oxides on silicon for novel devices”, by Vilquin et al. published in the 2011 1st International Symposium on Access Spaces, (ISAS), IEEE-ISAS 2011, pages 294 to 298, and “Integration of functional oxide thin film heterostructures with silicon (100) substrates”, published at URL: http://www.researchgate.net/publication/234300609 Integration of functional oxide thin film heterostructures with silicon (100) substrates, 1/2010.
The documents mentioned above do not, whether taken individually or in any combination with each other, disclose how to address the challenge(s) of integrating functional oxides with silicon photonics technology.